The present invention deals with silicone resin compositions which are curable at room temperature. More precisely, it deals with silicone resin compositions which can give a coating with excellent solvent resistance, mold release, water repellency, heat resistance, weather resistance and which have extended storage stability.
When organopolysiloxane resins containing hydroxyl groups bound to silicon atoms (hydroxylated silicone resins) are cured, traditional methods involve baking the resin at elevated temperatures. These temperatures are usually above 150.degree. C. and occasionally reach temperatures above 200.degree. C. Recently silicone resin compositions which are curable at room temperature has been proposed.
For example, room temperature curable resin compositions consisting of a hydroxylated silicone resin and an aminoalkylalkoxysilane, and of a hydroxylated silicone resin and an alkenylacetoxysilane were reported in U.S. Pat. No. 3,350,349 and U.S. Pat. No. 2,615,861, respectively.
However, when the solution of hydroxylated silicone resin with hydroxyl groups bound to silicon atoms is mixed with either an aminoalkylalkoxysilane or alkenylacetoxysilane, crosslinking occurs within a short time period and the storage stability is poor. In order to overcome such a drawback, there is a rigid requirement that these components should be mixed immediately before use. In such a case, the working time of the resin is very poor. The coating resin obtained by curing these hydroxylated silicone resins at room temperature, according to prior methods, have poor solvent resistance and they readily swell in solvents such as xylene and acetone.
Certain other methods were tried to overcome the drawbacks of the previously discussed prior art resins such as mixing alkoxysilanes and aminoalkylalkoxysilanes at a certain ratio with a hydroxylated silicone resin as reported in Japanese Pat. No. Sho 53[1978]-13,503.
Although the cured coating prepared from the composition set forth in Japanese Pat. No. Sho 53[1978]-13,503 does not swell in solvents such as xylene and acetone, it has some drawbacks, in that, the coating dissolves or peels off within 30 minutes after the coating is exposed to severe conditions, for example, immersion in 1,1,1-trichloroethane at 40.degree.-50.degree. C. and irradiation with ultrasonic waves and, in addition, the mold release property of the coating surface is poor.
The instant invention overcomes these problems. It was found that when an alkoxy-containing organopolysiloxane is compounded with the above-mentioned composition, a cured coating which has excellent storage stability and excellent solvent resistance and weather resistance, can be formed.
This invention therefore consists of a silicone resin composition comprising (A) 100 parts by weight of a hydroxylated organopolysiloxane of the general formula ##EQU1## wherein R.sup.1 is a substituted or unsubstituted monovalent hydrocarbon radical, n has an average value of from 0.80 to 1.80, p is an integer equal to or greater than 3, m has a value such that the total hydroxyl content of the organopolysiloxane is equal to or greater than 0.01 weight percent; (b) 0.5-150 parts by weight, per 100 parts of (A), of an alkoxylated organopolysiloxane of the general formula ##EQU2## wherein R.sup.2 has the same meaning as R.sup.1, R.sup.3 is a substituted or unsubstituted alkyl radical having 1-6 carbon atoms, a has an average value of from 0.40 to 1.70 q is an integer equal to or greater than 3, b has a value such that the total alkoxy content in (B) is equal to or greater than 5 weight percent; (C) 1-150 parts by weight, per 100 parts of (A), of an alkoxysilane of the general formula EQU R.sub.c.sup.4 Si(OR.sup.5).sub.4-c
wherein R.sup.4 has the same meaning as R.sup.1, R.sup.5 has the same meaning as R.sup.3, c has a value of 0.1 to 2 and, (D) 0.1-20 parts by weight, per 100 parts of (A) of an aminoalkylalkoysilane of the general formula ##STR1## wherein R.sup.6 is selected from a group consisting of the hydrogen atom, alkyl groups of 1-6 carbon atoms and aminoalkyl groups, R.sup.7 is a divalent hydrocarbon radical, R.sup.8 and R.sup.9 are alkyl groups of 1-6 carbon atoms, and d has a value of 0 or 1.
Component (A), the hydroxylated organopolysiloxane, can be any conventional organopolysiloxane resin. These materials are prepared generally by co-hydrolyzing chlorosilanes by conventional techniques.
For example, component (A) can be obtained by the hydrolysis of one or a mixture of two or more chlorosilanes having 0.8-1.8 organic radicals per silicon atoms in the presence of an organic solvent. Both an organopolysiloxane resin not subjected to any treatments after the hydrolysis and an organopolysiloxane resin in which a portion of the silanol groups have been caused to undergo condensation by heat treatment can be used in this invention. The amount of hydroxyl in the organopolysiloxane resin molecule must be equal to or greater than 0.01 wt%.
Examples of monovalent hydrocarbon radicals bound to the silicon atom are alkyl groups such as methyl, ethyl, propyl, tert-butyl, 2-ethylhexyl, dodecyl, 1-isobutyl-3,5-dimethylhexyl and octadecyl groups, alkenyl groups such as vinyl, allyl, and hexadienyl groups, cycloalkyl groups such as cyclopentenyl, cyclohexenyl, and cyclo-2,4-hexadienyl, aryl groups such as phenyl and naphthyl groups, aralkyl groups such as benzyl, phenylethyl and xylyl groups, alkaryl groups such as tolyl and dimethylphenyl groups, and halogenated monovalent hydrocarbon radicals such as chloromethyl, 3,3,3-trifluoropropyl, 3,3,4,4,5,5,5-heptafluoropentyl, perchlorophenyl, 3,4-dibromocyclohexyl, 2,2,2-trifluorotolyl, 2,4-dibromobenzyl, difluoromonochlorovinyl, .alpha.,.beta.,.beta.-trifluoro-.alpha.-chlorocyclobutyl and 2-iodocyclobutyl groups.
In order to obtain good mold release properties and water repellency on the coating surface, it is important to avoid the presence of more than 0.5 aryl groups bound to silicon atoms per silicon atom in the hydroxylated organopolysiloxane resin.
Component (B), the alkoxylated organopolysiloxane used in the present invention, can be obtained by the condensation of corresponding alkoxysilanes in the presence of an acid or alkali catalyst. In the condensation, the cocondensation of tetraalkylsilicates and titanate esters is contemplated by the invention. The amount of alkoxy groups bound to silicon atoms in the molecule must be equal to or greater than 5 wt% in the component (B). If there is less than the above-mentioned amount, a satisfactory solvent resistance cannot be obtained. The number of monovalent hydrocarbon radicals bound to the silicon atom must be 0.40 to 1.70 per silicon atom, and preferably 0.50 to 1.20.
The monovalent hydrocarbon radicals bound to the silicon atoms of the alkoxylated organopolysiloxane are those set forth above for component (A). The R.sup.3 group which forms the alkoxy group can be a substituted or unsubstituted alkyl group such as methyl, ethyl, propyl, tert-butyl, methoxyethyl, chloroethyl, .alpha.-ethylhexyl, dodecyl, 1-isobutyl-3,5-dimethylhexyl and octadecyl groups.
The amount of alkoxylated organopolysiloxane resin (B) ranges from 0.5 to 150 parts by weight per 100 parts by weight of component (A), and preferably from 1 to 70 parts by weight. If the amount is less than 0.5 part by weight, the solvent resistance of the coating is insufficient. If it exceeds 150 parts by weight, the coating becomes brittle.
Component (C), the alkoxysilane of the present invention, can be for example: methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, methyltri(methoxyethoxy)silane, dimethyldimethoxysilane, diethyldiethoxysilane, dipropyldimethoxysilane, methylethyldimethoxysilane, ethylpropyldimethoxysilane, propylmethyldimethoxysilane, dimethyldi(methoxyethoxy)silane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinylethyldimethoxysilane, vinylethyldi(methoxyethoxy)silane, vinylpropyldimethoxysilane, allyltrimethoxysilane, allyltriethylsilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropylmethyl-dimethoxysilane, methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate and hexyl orthosilicate.
The amount of alkoxysilane used in this invention generally ranges from 1 to 150 parts by weight per 100 parts by weight of component (A) and preferably from 5 to 80 parts by weight. If the amount is less than 1 part by weight, the storage stability of the composition is poor and the solvent resistance of cured coating is also poor. If it exceeds 150 parts by weight, the good storage stability is retained, but the drying properties, when it is applied as a coating, are poor.
Component (D), the aminoalkylalkoxysilane used in the present invention can be for example: .gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, .gamma.-(aminoethyl)-aminopropyltrimethoxysilane, methyl-.gamma.-aminopropyldimethoxysilane, methyl-.gamma.-(aminoethyl)-aminopropyldimethoxysilane and .gamma.-dimethylaminopropyltrimethoxysilane.
The amount of aminoalkylalkoxysilane present in this invention preferably ranges from 0.1 to 20 parts by weight per 100 parts by weight of component (A). If the amount is less than 0.1 parts by weight, it takes a long time for curing and the adhesion of the cured coating with the base material is poor. If it exceeds 20 parts by weight, the cured coating discolors, especially at high temperatures.
Organic solvents may be used in the present invention. They are not always needed if both components (A) and (B) have relatively low molecular weights. The application of the organic solvents is generally preferred because of the fact that component (A) is preferably diluted with the organic solvents before use. Also, the workability of the coated films is enhanced.
Aromatic, aliphatic and chlorine-containing solvents can be used as the organic solvents. Examples of aromatic organic solvents are benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene and ethylbenzene. Examples of aliphatic organic solvents are hexane, gasoline for industrial use, cyclohexane, methylcyclohexane and dimethylcyclohexane. Examples of chlorine-containing solvents are trichloroethylene, 1,1,1-trichloroethane, carbon tetrachloride and chloroform. Especially useful are the aromatic solvents such as xylene, toluene and benzene, which have a high solvation effect with respect to component (A).
In addition to the above-mentioned components (A)-(D), if desirable, .alpha.,.omega.-dihydroxydiorganopolysiloxane can be added in order to improve the mold release property. In such a case, the mold release property is improved as the amount of addition of .alpha.,.omega.-dihydroxydiorganopolysiloxane increases. On the other hand, the cured coat tends to become softer. Thus, the amount of this siloxane preferably ranges from 0.1 to 30 wt% per 100 parts by weight of component (A), if used. A catalyst can also be used in these compositions for the purpose of acceleration of the curing reaction. Appropriate catalysts are those which are ordinarily used in the dehydration condensation of silanol groups. Examples of such catalysts are the tin salts of carboxylic acids: dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dioctoate, stannous octoate, stannous naphthenate, stannous oleate, stannous isobutylrate, stannous linoleate, stannous stearate, stannous benzoate, stannous naphthoate, stannous laurate, stannous O-thymate, stannous .beta.-benzoylpropionate, stannous crotonate, stannous tropate, stannous p-bromobenzoate, stannous palmitooleate, stannous cinnamate and stannous phenyl acetate. In addition, a variety of pigments which are used in the common paints can be added.
The silicone resin compositions of this invention are characterized by the fact that they can form a hard coating by rapid curing at room temperature. The cured coating has excellent solvent resistance, mold release properties, water repellency, heat resistance and weather resistance. Thus, such compositions can be utilized in a wide range of applications. Examples of expected applications are coating agents for the purposes of release of oil, snow, ice, paints, dirt, foods, adhesives, tackifiers, mud, dust, raw rubber and latex; improvement of peelability and mold release; coating agents for the purposes of protection of the surface of various substances from the action of light, air, water, corrosive gases, corrosive liquids such as acids and alkalis, and various solvents; coating agents for the purpose of improvement in the surface electrical characteristics, especially the electrical insulation properties of various substances; and coating agents for the purpose of reducing the liquid viscosity resistance acting on an interface in contact with a liquid.
Almost any type of substrate can be coated. Examples of such substrates are: metals, plastics, ceramics, glass, wood, rubber, mortar, concrete, brick, tiles and slate. Specific examples of such applications are automobiles, ships, metal dies, cooking utensils, food containers, electric poles, guard rails, road signs, relays, terminals, insulators, spark plugs, printed base plates, electric contacts, electric wires, interior or exterior surfaces of pipes used for carrying liquids, bridge beams, buildings, tile joints, various types of apparatii and their parts, engines, mudguards, window glasses and the prevention of water leakage from reservoirs.